Filters of a variety of types have heretofore been proposed for filtering fluids. Filters are known which comprise a housing for permitting the passage of fluid and a filtering medium mounted in the housing. The housing is air-tight so that no fluid leaks during the use, and is made unitary by ultrasonic melt-adhesion or like methods.
U.S. Pat. No. 3,932,153 discloses a filter which is effective in controlling, particularly, bacteria. As shown in cross section of FIG. 6, the filter 20 comprises a combination of a pair of conical flow path members 21 and 31 with flanges 22 and 32. The flanges which are joined together to form a housing and a flow path 23 is formed in the housing to permit the passage of fluid. The fluid flows as indicated by arrows. The flanges 22 and 32 are bonded together by ultrasonic melt-adhesion with a filtering medium 24 sandwiched therebetween, forming an air-tight housing. In order that the flanges of the filter can be easily positioned at the time of bonding while stretching the filter medium, one flange is provided with a V-shaped groove 25 and a concave groove 26 and the other flange is provided with a corresponding triangular projection and a convex projection. A similar filter has also been disclosed in European Patent Application Laid-Open No. 0.265,163.
In the journal KOKYU, "Effectiveness of a Filter for Spirography in Inspecting Lung Function", Vol. 14, No. 6, PP. 641-645, 1995, Nishimura et al. teaches the effectiveness of using a filter for spirography in an apparatus for measuring lung function. This is because, when the human breath is directly introduced into a measuring apparatus, bacteria contained in the breath, saliva and sputum enter into the circuitry in the apparatus, adversely affecting measurements. Or, when the apparatus is used repetitively, the human body may be infected with contaminated substances in the apparatus. The filter for spirography used in this apparatus is a special filter, C-8F (part number), manufactured by Chest MI Co., and its use is shown in FIG. 1 on page 642 of the journal KOKYU. Though not described in detail in the KOKYU, this filter is made of a plastic material and contains a pleated mesh-like filtering medium to enhance filtering efficiency. The housing of this filter is fabricated relying on ultrasonic melt adhesion.
When used for the medical measuring apparatuses such as artificial respiratory machines, anesthetic machines, machines for measuring function of lung, spirometers, etc., the above mentioned filter and other conventional filters are effective in removing bacteria, saliva and sputum from the human breath, making it possible to prevent the apparatuses from being contaminated with bacteria. Or, when the apparatuses are contaminated, on the other hand, such filters make it possible to prevent the human body from being infected with bacteria.
However, the above conventional filters are cumbersome to produce and are costly since the housing is formed into a unitary structure by ultrasonic melt adhesion or the like. According to the above-mentioned KOKYU, a disposable mouth piece that is discarded after each use costs 20 yen per piece, whereas a filter costs 290 yen per piece. Besides, since the filtering medium is firmly secured, the filter body, too, must be discarded when the filtering medium is contaminated, which is not economical. In particular, when the user of the filter is an infected patient, the filter must be discarded even though the filter body has not been contaminated, which is disadvantageous.
The object of the present invention is to provide a filter frame which can be repetitively used and can be easily manufactured being free from the above-mentioned inherent problems.
Another object of the present invention is to provide a filter for filtering fluid which is cheaply obtained and can be repetitively used upon renewing the filtering medium.
A further object of the present invention is to provide a filter which permits the filtering medium to be easily renewed on site where it is used even by a person who is not skilled at renewing filtering medium.
Other objects of the present invention will be easily understood from the following detailed description of the invention.